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Drafting

A T-square is used as a guide for drawing horizontal lines and as a support for the triangles which, in turn, are used as guides for drawing vertical and inclined lines. To use a T-square or triangle as a guide for drawing lines, pull the pencil along the edge of the straight edge from left to right. (These directions are for right-handed people. Left-handed people should reverse the directions.) Rotate the pencil as you draw so that a flat spot will not form on the...

The baseline system of dimensioning is illustrated in figure 73 (on the previous page) . All dimensions in the same plane are located from the same line which is called a baseline. It is sometimes called a reference line or datum line. This system is particularly useful because it eliminates tolerance buildup, it is easy for manufacturers and inspectors to follow, and it is easily adaptable to the requirements of numerical tape machines. Its chief disadvantage is that the...

ISOMETRIC, OBLIQUE, AND PICTORIAL DRAWINGS. The basic reference system for oblique drawings is shown in figure 56 (on the following page). The most distinct characteristic of the oblique axis is the 90 relationship between the left-hand axis and the vertical axis. Because of this 90 relationship, the front view and all surfaces parallel to it are almost identical to the front view of an orthographic drawing. This makes it very easy to transfer information between the two different front views.

SCALE 2-1 SCALE 1-1 SCALE-1-2 The scale note 1 2 means that every 1 2 inch on the drawing is actually 1 inch on the object. In other words, the drawing is one-half the size of the true object size. Similarly, the scale note 2 1 means that 2 inches equal 1 inch thus, the drawing is twice as large as the actual object. The note 1 1 means that the drawing is the exact same size as the object. This concludes this subcourse dealing with the principles of drafting and shop drawing. In this subcourse,...

The basic reference system for isometric drawings is shown in figure 36 on the following page . The three lines are 120 apart and may be thought of as a vertical line and two lines 30 to the horizontal, which means that they may be drawn by using a 30-60-90 triangle supported by a T-square. All isometric drawings are based on this axis system.

Figure 64 on the following page is the solution and was derived by performing the following stets Step 1. To the best of your ability, make a freehand sketch of the solution view A . Step 2. Using very light lines, lay out a rectangular box whose height, width, and length corresponds to the height, width, and length given in the orthographic views. In this example, a basic cylinder shape was substituted for the rectangular shape views B, C, and D . Step 3. Using very light lines, lay out the...

Figure 61 on the following page is the solution for this problem and was derived using the same procedures as for normal surfaces. Step 1. To the best of your ability, make an oblique freehand sketch of the proposed solution view A . Step 2. Using very light lines, lay out a rectangular box whose height, width, and length correspond to the height, width, and length given in the orthographic views. In this case, a receding axis of 30 was chosen view B . Step 3. Using very light lines, lay out...

Point is marked 0, and the two intersections are marked points 1 and 2 figure 51, view A . Step 2. Draw a rectangular box and transfer the points 1, 2, and 0 to the front plane of the isometric drawing views B and C . Step 3. Project the points in the front plane across the isometric drawing to the back plane view D , and label them 3, 4, and 5. Step 4. Align the proper hole in the isometric ellipse template with the center lines on the front of the isometric surface, and draw in the isometric...

Figure 13 on the following page shows the solution, which was derived at by the following Step 1. Identify the lines that define plane 1-2, 2-4, 4-3, and 3-1. Step 2. Project the individual points 1, 2, 3, and 4 into the right side view. Step 3. Draw in, with object lines, the lines that define the plane. The lines drawn in step 3 define the right side view of plane 1-2-3-4. In line theory we found that the end view of a line was a double-point. A similar situation appears in the plane theory,...

Figure 66 on the following page illustrates a full-oblique sectional view, and figure 67 on the following page illustrates a halfoblique sectional view. Oblique sectional views are drawn in the same sectional views are drawn. Since the only difference between the two sectional views is the defining axis system, the information given in paragraph 2f, page 63, may also be applied to oblique sectional views.

Erase all lines and smudges, check your work, and draw in all lines to their final color and configuration figure 59, view E . b. Inclined and Oblique Surfaces. Figure 60 on the following page is a sample problem that involves creating an oblique drawing from given orthographic views that contain an inclined surface. Unlike isometric drawings, angular dimensions may be directly transferred from the front orthographic view to the front oblique view, thereby eliminating the need for...

In the hole-to-hole system, all dimensions in the same plane are measured for the lines that define the critical holes. The baseline is not, in this case, a physical line, but is the center line between the critical holes. 8 Coordinate System. The coordinate system is a dimensioning system based on the mathematical x-y coordinate system. It is usually only used to dimension an object that contains a great many holes, for example, an electrical chassis. It is particularly well-suited to computer...

Isometric drawings may be dimensioned by using either the aligned system or the unidirectional system. Regardless of the system used, the leader lines must be drawn in the same isometric plane as the surface they are defining. The guidelines for the dimensions in the aligned system are drawn parallel to the edge being defined, while the guidelines for the unidirectional system are always horizontal. Figure 53 on the previous page is another example of the unidirectional...

Figure 40 on the following page is a sample problem that involves the creation of an isometric drawing from given orthographic views that contain a slanted surface. The slanted surface is dimensioned by using an angular dimension. That presents a problem because angular dimensions cannot be directly transferred from orthographic views to isometric drawings.

Normally, an isometric drawing is positioned so that the front, top, and right side views appear, as shown in figure 37 on the following page . This may be varied according to the position that the draftsman feels best shows the object. Dimensional values are transferable from orthographic views only to the axis, or lines parallel to the axis, of isometric drawings. Angles and inclined dimensional values are not directly transferable and require special supplementary layouts which will be...

To determine exactly if and how much of the bottom edge of the hole should be drawn, locate the center point of the hole on the bottom surface and draw the hole by using the same procedure you used for the hole on the top surface. If the hole drawn on the bottom surface appears within the hole on the top surface, it should appear on the finished drawing. If the hole drawn on the bottom surface does not appear within the hole on the top surface, it should not appear on the finished drawing....

In the machine shop, the sketch or freehand drawing is a quick, accurate, and clear method of conveying ideas. Although sketching is not essential to the reading of a shop drawing, it is helpful in learning the language of mechanical drawings. Sketches are made rapidly and usually without the aid of drawing instruments, but they must be accurate and complete. Omissions and mistakes that would be discovered in making a scale drawing might easily be overlooked in a freehand sketch. Extreme care,...

Draw in the hexagon figure 31, view C . e. Pentagon, figure 32 on the following page . In the following subparagraphs, we will discuss the procedures for constructing a pentagon. We have to draw a pentagon inscribed in a circle of diameter A. To draw this pentagon, perform the following steps Step 1. Construct a circle of diameter A. Step 2. Define points 0, 1, and 2 as shown in view A. Step 3. Bisect line 0-1 and define the midpoint as point 3 figure 32, view A . Step 4. Define point 4...

To transfer an angular dimensional view from an orthographic view to an isometric drawing, convert the angular dimensional value to its component linear value and transfer the component values directly to the axis of the isometric drawing. Figure 41 on the previous page illustrates this procedure by showing two angular dimensions that have, been converted to their respective linear values, then showing how these values are transferred to the isometric axis. Normally, a draftsman simply measures...

5 Dimensioning Small Distances and Small Angles. When dimensioning a small distance or a small angle, always keep the lettering at the normal height of either 1 8 or 3 16. The temptation is to squeeze the dimensions into the smaller space. This is unacceptable because crowded or cramped dimensions are difficult to read, especially on blueprints which are microfilmed. Figure 72 on the following page shows several different ways to dimension small distances or angles and still keep the...

The receding lines may be drawn at any convenient angle. Upward and to the right at either 30 or 45 are most commonly used because these angles may be drawn with standard triangles. The choice of which receding angle to use depends on which angle best shows the object involved. Dimensional values are directly transferable from the front view of the orthographic drawing to the front view of the oblique drawing. Circles transfer as circles, not as ellipses as in isometric drawings, and angles...

The table may also be used in reverse. If you know what your given design requirements are, look up these values in the table to find which part number you should call out on the drawing. 10 Irregularly Shaped Curves. To dimension an irregularly shaped curve, dimension the points that define the line. The more points you dimension, the more accurate will be your definition. Figure 77 on the previous page illustrates a dimensioned irregularly shaped curve. b. Tolerances. No dimension can be made...